<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<script type="text/javascript">
			/* undefined==null;
			=== ,!==全等跟不全等,只要类型不同就直接为return false;
			NaN不等于NaN;
			isNaN能判断是否为NaN,也会进行类型转换
			 */
			
			console.log(undefined==null);
			
			console.log("123"===123);
			
			console.log(NaN==NaN);
			
			var a="hello";
			console.log(isNaN(a));
			
			var b="123";
			console.log(isNaN(b));
		</script>
	</head>
	<body>
	</body>
</html>